This invention pertains to electromagnetic circuits, and in particular to circuits which provide magnetic excitation according to a cyclic pattern. One example of cycling electromagnetic fields is found in particle accelerators having a defined particle path, such as a circular ring or "racetrack". Acceleration is typically provided by a plurality of spaced-apart radio frequency resonating cavities which are placed about the ring. Thus, a particular particle or associated group or bunch of particles is accelerated in discrete bursts as it travels around the ring, typically at speeds approaching the speed of light. Particles traveling in the ring are subjected to centripetal forces during particle acceleration. If the particle beam is to be confined within the ring, these centripetal forces must be precisely balanced. The force balancing necessary for particle control is provided by electromagnets located adjacent the several accelerating portions of the ring.
In one type of accelerator, the Rapid Cycling Synchrotron (RCS) located at Argonne National Laboratory, discrete bunches of protons are accelerated for delivery at a designated target. The magnetic confinement of a particular proton bunch must be coordinated with the bunch's injection and ejection from the machine, as well as the duration of residence therein. Such coordination should include a relatively time-invariant magnetic guide field during injection to optimize capture efficiencies. A "flat" magnetic guide field is often also desirable at the end of the acceleration period to eject the particles in discrete bunches during the beam spill time. While protons have been successfully accelerated at pulse repetition rates of 30 pulses per second, an economical means of upgrading the machine by increasing the pulse repetition rate so as to satisfy demands for increasing particle intensity, has been sought.
Economical designs of new machines, as well as the upgrading of existing installations, focus on the maximum pulse repetition rate that can be obtained from a system of given cost. The tradeoff involved in such designs centers around a balance of radio frequency accelerating voltage and the time rate of increase of the magnetic confinement field. Higher pulse repetition rates require more rapid cycling of the magnetic confinement fields of the machine. The shortening of the confinement field rise time, however, requires costly higher voltage rf accelerator equipment.
It is therefore an object of the present invention to provide an economical control circuit, comprised of relatively low-cost components, which energizes and resets an electromagnet in a rapid cyclic pattern.
It is another object of the present invention to provide a control circuit of the above-described type which offers a relatively high pulse repetition rate and which is compatible with relatively low-cost radio frequency accelerator systems.
A further object of the present invention is to provide a control circuit for generating relatively time-invariant operating portions at predetermined points on the rapid cyclic pattern.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.